I have taken sand paper to a couple factory AR triggers with very good results. The sear angle on the trigger makes the trigger have to push the hammer back to be pulled. That makes for a heavy and gritty trigger pull. Changing the angle lowers the trigger pull and smooths it out considerably. I only work on the trigger, not the cut on the hammer.
I can get a smooth 5.5# pull and keep it safe. I have fired many rounds through them will no trigger slip or doubling.
Just some advice for people who are considering doing this: mil-spec AR triggers are case hardened - meaning the outer layer is harder than the core. When sanding, stoning, etc on any AR FC parts, you can introduce new points of failure by going through the hardened section into the soft. All will seem well at first but a trigger that could and probably would have lasted you 10,000 rounds will probably give up the ghost after less than half that many.
You're better off buying an ALG QMS for $45.
Anyway, like some of you, I made my own "night sights". The white sight paint on my old XD-45C had turned permanently yellow due to powder residue, so I used a dental pick (that's not paint in there!) to carefully pick out all of the factory "gunk", then mixed up some Glow Inc. Ultra G-10 green with some epoxy and painstakingly filled in the holes dab at a time. Then, just because I'm paranoid like that, I sealed each dot with a small dab of super glue after the epoxy set. I did that about a year and maybe 500-600 rounds ago and it's still holding up.